Method and means for antenna coupling

ABSTRACT

An improved antenna coupler including reactive elements for translating antenna impedance to a resistance load, and an autotransformer for transforming the resistance load to a resistive level for matching with the resistance of said radio means, said autotransformer comprising a magnetic core and a coil having a plurality of turns, tap contacts to selected turns of said coil and switch means for connecting one of said taps to said antenna and for connecting another of said taps to said inductive means.

United States Patent [191 Frazier METHOD AND MEANS FOR ANTENNA COUPLING [75] Inventor:

[22] Filed: Nov. 6, 1972 [21] Appl. No.: 303,745

Melvin A. Frazier, Marion, Iowa [.4 1 Nov. 27', 1973 OTHER PUBLICATIONS The A.R.R.L. Antenna Book The American Radio Relay League, Inc. West. Hartford, Conn. 1956; TK6565A6A6; pp. 29, 30, 59 60 and 182-185. v

Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Marvin Nussbaum Attorney-Henry K. Woodward et a1.

[57] ABSTRACT An improved antenna coupler including reactive elements for translating antenna impedance to a resisplurality of turns,- tap contacts to selected turns of said I coil and switch means for connecting one of said taps to said antenna and for connecting another of said taps to said inductive means.

3 Claims, 3 Drawing Figures 509 INPUT TRANS" MITTER [52] U.S. Cl. 333/32, 343/745 [51] Int. Cl. H0311 7/38 [58] Field of Search 333/32, 17;

[56] References Cited UNITED STATES PATENTS 1,880,198 10/1932 Gebhard 343/822 X 2,002,844 5/1935 Aceves et a1. 343/860 X 2,207,246 7/1940 Fischer 343/745 2,745,067 5/1956 True et a1. 333/17 2,981,902 4/1961 Familier 333/17 M 3,129,386 4/1964 Daly 325/174 FOREIGNP-ATENTS 0R APPLICATIONS 633,975 12/1949 Great Britain .1 333/32 60 Q, I N P U T ANTENNA PAIENIEDHUVZTIQTS R E R E E WC E DH T R G am 2 w U cr FIG. 1

K T TRANSLATION K TRANSLATION 2' TRANSLATION INPUT TRANS- MITTER FIG. 2

M QTN ONE 6 T WN FIG. 3

METHOD AND MEANS FOR ANTENNA COUPLING The use of antenna couplers to provide impedance matching between an antenna and a transceiver is well known in the art. Typically, capacitive means is provided to adjust the antenna impedance to a desired impedance range, inductive means is employed to eliminate the capacitive reactance, and a final tuning stage adjusts the remaining load to the required ohmage to achieve a desired voltage standing wave ratio for a given operating frequency when connected to the transmitter-receiver.

Conventionally, the final tuning stage comprises two servo controlled analog tuning elements such as a variable coil or capacitor to provide the necessary phasing and loading for the desired VSWR, typically 1.3:l.0 or less. Such a tuner is relatively expensive.

An object of the present invention is an improved antenna coupler which is more economical.

Another object of the invention is an antenna coupler which may be digitally controlled.

Still another object of the invention is a digital tuning transformer for use in an antenna coupler.

Another object of the invention is an improved and economical method of coupling and impedance matching an antenna to a radio transceiver.

Features of the invention include a tapped autotransformer, in combination with variable capacitive and inductive means, for transforming an antenna reactance to a desired resistive level for impedance matching. Means is included for adjusting the transformation digitally.

The invention and objects and features thereof will be more fully understood from the following detailed description and appended claims when taken with the drawing, in which:

FIG. 1 is a functional schematic diagram of an antenna coupler;

FIG. 2 is a plot of impedance translation'by the antenna coupler of FIG. 1 in accordance with the present invention; and

FIG. 3 is a schematic of an autotransformer useful in an antenna coupler in accordance with the present invention.

Referring now to the drawings, FIG. 1 is a functional schematic diagram of an antenna coupler. The coupler shown generally at provides the necessary impedance matching between antenna 12 and a transmitterreceiver 14..To permit. satisfactory and efficient operation of the transmitter 14, the antenna coupler 10 must translate the impedance of antenna 12 sufficiently close to the output impedance of the transmitter to effect a given voltage standing wave ratio, typically 1.3:l.0 or less.

The conventional antenna coupler includes a shunt variable capacitor 16 connected to antenna 12 with a serial variable capacitor 18 interconnecting antenna 12 through a variable inductor 20 to a coupler tuning network 22. For highly capacitive antennas, such as whip antennas, a variable inductor may be serially connected between antenna 12 and shunt capacitor 16. Further, the reactive tuning elements 16 and 18 may be of opposite reactance, i.e., inductors rather than capacitors, if

their impedance translation is desired to be inductive. Variable inductor 20 must then be replaced by a variable capacitor.

Conventionally, coupler network 22 comprises two servo controlled analog tuning elements which can translate an input impedance within a limited range to the .necessary impedance for matching with the transmitter or receiver. Shunt capacitor 16 and serial capacitor 18 cooperatively function to adjust the impedance of antenna 12 to within the limited tuning range. However, the impedance translation effected by capacitors 16 and 18 normally has a capacitive reactance element which must be cancelled by variable inductor 20 in series therewith.

This impedance translation of the antenna coupler is illustrated in the plot of FIG. 2 in which resistance is measured along the abscissa and positive and negative reactance is measured along the ordinate. As illustrated, the variable capacitors translate the antenna impedance to within the shaded area 30 defined by 0 to 60 ohms resistance and 0 or negative reactance. Assuming that. .the variable capacitive translation produces an impedance defined by point 32, the variable inductor effects a translation of the impedance to a pure resistance at point 34. Thereafter, the coupler tuning network 22 translates the resistance at point 34 to a required resistance level to satisfy the desired voltage standing wave ratio. For a VSWR of 1.2: l .0 and an antenna impedance of 50 ohms, the necessary resistance tuning range is from 42 to ohms.

As above noted, the conventional tuning network employing servo controlled tuning elements adds considerably to the cost of the antenna coupler. In accordance with the present invention, such servo controlled means is replacedby an autotransformer having multiple taps to effect a required impedance transformation. FIG. 3 is a schematic of one embodiment of such an autotransformer and includes a coil 40 consisting of nine turns with taps taken at the third, fourth, sixth, seventh,

eighth, and ninth turns. Assuming the translations described with reference to FIG. 2, the input from the antenna, translated to be less than 60 ohms resistive is applied at point 42 and is selectively connected through relays A, B, and C to the tap at the second, third, fourth, or sixth turns of transformer coil 40. Similarly, the 50 ohm input from the transmitter is connected at point 44 selectively through relays D, E, and F to the tap at the seventh, eighth, and ninth turns of transformer 40. Thus, in this illustrative embodiment, the translated antenna input impedance of less than 60 ohms is transformed with transformer 40'to within the requisite resistance range to effect a 1.2:].0 VSWR when connected to the transmitter. As described above, for coupling into a 50 ohm transmitter input the requisite impedance range is 42-60 ohms. Thus, assuming that the translated antenna input at point 42 lies within this range, then relays A and F are energized to bypass the transformer 40. Assuming that the antenna input resistance lies outside of the requisite range of 42-60 ohms, relays B, C, D, and E are energized to effect the necessary transformation in accordance with the following table:

60 ohms. Consequently, the autotransformer 40 is required only for a step up of resistance. It will be appreciated that if a step down in resistance were required, relay means may be added to reverse the antenna input and transmitter input to the autotransformer.

It will be further noted from the above table that the step up resistance range for succeeding transformer ratios overlap. In the overlapping portions of adjacent transformer ratios either of the connections effected by selective closing of relays B, C, D, and E may be employed, or alternatively, the relays may be preprogrammed to achieve minimum VSWR for the resistances within the overlapping portions of the resistance range.

In one embodiment of the autotransformer using nine turns of number 16 buss wire, the magnetic circuit comprises a pot core made of Indiana General Ferramic Q2 material. It will be appreciated that other magnetic circuits such as a toridal core may be employed. Further, the relays of the illustrative embodi ment in FIG. 3 may be replaced by switching diodes to achieve solid-state tuning. In an HF frequency application the value of the shunt capacitor was 12-2l5 pfd, the value of the series capacitor was 28-215 pfd, and the value of the variable inductance was 0.5-165 uh. Additionally, a series inductor was connected with the antenna which was -80 uh.

An antenna coupler employing an autotransformer in accordance with the present invention has performed with very good results and with a very significant cost savings over conventional analog tuning antenna couplers. While the invention has been described with reference to specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the scope of the invention. Various modifications and changes may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.

I claim:

1. Means for coupling an antenna to radio means comprising reactance means for translating the antenna impedance to a resistance load having no reactive component, and autotransformer means for transforming said resistance load to aresistive level for matching with the resistance of said radio means, said autotransformer comprising a magnetic core and a coil having a plurality of turns, tap contacts to selected turns of said coil, first switch means connectable to a first plurality -of said tap contacts, second switch means connectable to a second plurality of said tap contacts, and third switch means for reversibly switching said first and second switch means to said antenna and to said reactance means whereby a range of transformation ratios are available and said resistive load may be increased and decreased as required for impedance matching.

2. A coupler for coupling and impedance matching a transceiver to an antenna comprising capacitive means for translating the antenna impedance to within a limited impedance range with a negative reactance component, inductive means connected to said capacitive means for eliminating said negative reactance component and producing. a resistive load, and autotransformer means for transforming said resistive load to a resistive level for matching with the transceiver resistance, said autotransformer comprising a magnetic core and a coil having a plurality of turns, tap contacts to selected turns of said coil, first switch means connectable to a' first plurality of said tap contacts, second switch means connectable to a second plurality of said tap contacts, and third switch means for reversibly switching said first and second switch means to said antenna and to said inductivemeans whereby a range of transformation ratios are available and said resistive load may be increased and decreased as required to transform to said resistive level.

3. A coupler as defined by claim 2 wherein said capacitive means comprises a variable shunt capacitor and a variable series capacitor. 

1. Means for coupling an antenna to radio means comprising reactance means for translating the antenna impedance to a resistance load having no reactive component, and autotransformer means for transforming said resistance load to a resistive level for matching with the resistance of said radio means, said autotransformer comprising a magnetic core and a coil having a plurality of turns, tap contacts to selected turns of said coil, first switch means connectable to a first plurality of said tap contacts, second switch means connectable to a second plurality of said tap contacts, and third switch means for reversibly switching said first and second switch means to said antenna and to saiD reactance means whereby a range of transformation ratios are available and said resistive load may be increased and decreased as required for impedance matching.
 2. A coupler for coupling and impedance matching a transceiver to an antenna comprising capacitive means for translating the antenna impedance to within a limited impedance range with a negative reactance component, inductive means connected to said capacitive means for eliminating said negative reactance component and producing a resistive load, and autotransformer means for transforming said resistive load to a resistive level for matching with the transceiver resistance, said autotransformer comprising a magnetic core and a coil having a plurality of turns, tap contacts to selected turns of said coil, first switch means connectable to a first plurality of said tap contacts, second switch means connectable to a second plurality of said tap contacts, and third switch means for reversibly switching said first and second switch means to said antenna and to said inductive means whereby a range of transformation ratios are available and said resistive load may be increased and decreased as required to transform to said resistive level.
 3. A coupler as defined by claim 2 wherein said capacitive means comprises a variable shunt capacitor and a variable series capacitor. 